1. Technical Field
The present invention relates generally to fuel cell, and more particularly to a modular fuel cell structure, a casing of the modular fuel cell structure, and a fuel cell system.
2. Description of Related Art
After the industrial revolution in the nineteenth century, fossil fuels have become the main energy source. In addition to providing a vast amount of energy for humanity, an enormous amount of plastic products is also manufactured by using the abundant oil, coal, and natural gas on the planet. However, the cheap petrochemical energy will eventually dry up, and the world is bound to face the impact of high oil prices caused by the reduction of petrochemical capacity in the future. How to reduce the reliance on fossil fuels and appropriately use limited energy has become one of the important issues in energy policy for the whole world.
In addition to energy and economic issues, environmental issues have also received considerable attention in the international community in recent years. The problem of the greenhouse effect has been highly concerned for decades. Besides that, the heat island effect in metropolitan areas will become increasingly severe along with the development of megacities, and microscopic particles suspended in the air (e.g., PM 2.5) will also directly affect human health. Therefore, after the World Wide Views on Climate and Energy, how to provide high-performance, low-pollution energy in metropolitan areas will be an urgent and important issue for every country in pursuit of sustainable development.
Metal fuel cells have extremely high volumetric and gravimetric specific energy, and therefore are an excellent energy solution. Among the various types of metal fuel cells, zinc fuel cells have attracted particular attention since zinc in aqueous solutions and alkaline electrolytes is stable.
At present, products and related studies of zinc fuel cells all use porous zinc plate or zinc particles as the anode fuel of a battery. During the process of discharging, the reaction area of a zinc plate gradually reduces because the surface thereof reacts to become zinc oxide. As a result, the battery performance gradually reduces as well. Furthermore, the zinc anode plate of battery has to be replaced in mechanical ways after the reaction is completed, which is very inconvenient. Therefore, in order to make zinc fuel cells more practical and convenient, the form of the zinc anode thereof and the way of removing reactants must be improved.
Primary zinc-air batteries are still the only type available on the current market, which are mainly used in the hearing aids and other equipment. On the other hand, the development of secondary zinc-air batteries is still in a bottleneck, and therefore are not widely used in personal medical aids and energy systems yet. Strictly speaking, the reasons may include the following:
1. Air cathode has poor discharge power.
2. Isolation membrane has poor ionic conductivity.
3. Zinc anode cannot operate for a long time.
4. Zinc particles cannot be fully utilized as fuel.
5. The interrelated relationship between air, water and heat management system, and voltage monitoring technology still has to be integrated.
The above-described points 1 and 2 are common problems for various types of fuel cells. In recent years, as the material technology has matured, better reduction effect has been achieved for catalysts of non-precious metals and conductive materials on the air electrode, which significantly improves the efficiency of the reduction reaction. Also, regarding the separating membrane, the materials and ionic conductivity are greatly elevated as well, so that the conductive properties of the separating membrane are much better than ever.
In addition, the design of conventional fuel cells has one single fuel inlet and one single fuel outlet, and metal particles are mixed with an electrolytic solution before being injected into the reaction vessel for reaction while in use. However, with such design for battery structure, the injected fuel may not be evenly mixed, causing low performance for fuel cells. In other words, the ratio of metal particles to an electrolytic solution for the electrochemical reaction is difficult to manipulate as appropriate, for the injected electrolytic solution which contains metal particles may be mixed unevenly. As a result, there might be no sufficient metal particles in a fuel cell for reaction, leading to poor efficiency.
Thus, conventional fuel cells still have many challenges to be overcome.